The present invention generally relates to image recording apparatuses and more particularly to a sheet feed mechanism for use in an image recording apparatus such as a printer, copier, facsimile, or the like. Specifically, the present invention relates to a sheet feed mechanism of an image recording apparatus for use with a cassette that has a movable sheet plate for holding a sheet thereon, wherein the sheet feed mechanism pushes the sheet plate of the cassette in the upward direction to urge the sheet held thereon against a feed roller and for feeding the sheet to the image recording apparatus one by one by driving the feed roller.
FIG. 1 shows a conventional construction of a sheet feed mechanism for use in an image recording apparatus.
Referring to FIG. 1, the sheet feed mechanism is provided inside the body (not shown) of the image recording apparatus and cooperates with a cassette 6 that has a body 6a. The sheet feed mechanism includes a rotary shaft 1 held rotatably on the body of the apparatus and carries at both ends thereof a pair of levers 2 and 3. Further, there is provided a central lift arm 4 of which action will be described later. The lever 2 generally has an L-shape wherein a first end thereof is connected to a spring 5 that urges the lever 2 continuously to rotate in the counter-clockwise direction.
The cassette 6, on the other hand, includes a sheet plate 7 on which a stack of sheet P is placed. The plate 7 is hinged to the body 6a at an end not shown in FIG. 1 and is movable up and down about the hinge. At the front end of the body 6a, there is provided an opening 8 for accepting the arm 4 when the cassette 6 is mounted on the image recording apparatus, and a cam part 9 is formed on the outer surface of both side walls of the body 6a to guide the levers 2 and 3.
Upon mounting of the cassette 6 on the recording apparatus, the cam part 9 at both side walls of the cassette body 6a is engaged with a projection 2a formed at a second, opposite end of the lever 2 as well as with a projection 3a that is formed at an end of the lever 3. With further insertion of the cassette 6, the cam part 9 moves the arms 2 and 3 in the clockwise direction and the lift arm 4 is lowered accordingly. Thereby, the lift arm 4 is accepted by the cassette 6 through the opening 8 at the lower side of the sheet plate 7. With further insertion, the arms 2 and 3 are disengaged from the cam part 9 and are rotated in the counter-clockwise direction by the action of the spring 5. It should be noted that the rotation of the arms 2 and 3 can be very fast due to the large urging force exerted by the spring 5. In response to the rotation of the arms 2 and 3, the lift arm 4 pushes the sheet plate 7 strongly in the upward direction by a contact part 4a formed at the tip end of the arm 4. As a result, the sheet P held on the plate 7 as a stack is urged firmly against a feed roller (not shown) of the apparatus that is provided above the cassette 6, and the sheet is fed by the feed roller one by one for image recording.
In this conventional sheet feed mechanism, however, there arises a problem that the movable sheet plate 7 may cause a deformation due to the large impact given by the lift arm 4 when it goes up and hits the bottom of the plate 7. Thereby, the sheet held on the plate 7 may cause a corresponding bending. Such a bending of the sheet stack P tends to cause a jamming of the sheet.